Grammar moment: when to put commas around descriptive elements

This is a common problem: You’re writing a sentence, and you have a descriptive word, phrase, or clause. You know that sometimes you’re supposed to separate those words with commas, but sometimes you’re not. You vaguely remember some lesson you got from some English teacher sometime in the distant past, involving “restrictive” and “non-restrictive” something-or-other, but you can’t even remember what those terms mean, let alone how they relate to commas.

Here’s the good news. The actual rule is pretty simple: If a descriptive element contains “extra” information that can be removed without changing the meaning of the sentence, separate it from the rest of the sentence with commas. If removing the element DOES change the meaning, don’t use commas. You don’t need to remember the technical terms unless you have a grammar teacher who makes you memorize them. (If that’s the case, be aware that the terms are confusing, since “non-restrictive” refers to where you DO use commas, while “restrictive” refers to when you DON’T.)

Let’s look at a couple of examples.

Edgar brought his wife, Cleo, to the party.

In this case, we know Edgar brought his wife to the party, and her name is extra information. If we remove it, we still know that Edgar brought her to the party. On the other hand, if we remove the commas, we end up with something different.

Edgar brought his wife Cleo to the party.

Now the wife’s name is not extra information. This means Edgar has more than one wife, and since we need to know which one he brought, we don’t put commas around her name.

Here’s another example:

The town built a memorial to all of the people, who were killed by drunk drivers.

In this case, the town built a memorial to all of the people. It’s just a little bit of extra information that all of the people were killed by drunk drivers. Of course, that means this is now a ghost town, so one is left to wonder who built the memorial.

The town built a memorial to all of the people who were killed by drunk drivers.

This makes more sense. The memorial is not to everybody in the town, because not everybody in the town was killed by drunk drivers.

One other issue to note: when you use commas to separate an element, you MUST put commas BOTH before and after the element you’re separating, unless it’s already at the end of the sentence. Otherwise, your reader can get really confused trying to figure out where the extra information ends and the main part of the sentence resumes.

There’s another related issue – when you have a descriptive element that begins with who, which, or that, which one do you use?

First, when you’re referring to a person, you can use either who or that, although who is generally preferred (and some grammar teachers will insist that who is the only word to use for people). Things can be referred to as either that or which. People are NEVER referred to as which.

In the U.S., the convention (it’s not a rule, although some grammar teachers may try to tell you it is) is to use that for clauses that don’t use commas (restrictive clauses) and which for clauses that do use commas (non-restrictive clauses). In Britain, the convention is the opposite.